The GeForce GTX Titan blew us all away eight months ago with its mindblowingly fast GPU. The catch, of course, was that Nvidia wanted $1,000 for it. In a sense, the Radeon R9 290X could be considered AMD's Titan, as it takes the Tahiti architecture and stuffs with nearly 2000 million more transistors.
It's the most complex and powerful GPU AMD has created and by no coincidence, it's also one of the most expensive, but before you click away, that's "only" $550, which is substantially cheaper than Nvidia's solution.